This invention relates to an enthalpy calculator in which the enthalpy of a body of gas or humid air is calculated by an arithmetic unit in accordance with an enthalpy equation from the measured temperature and relative humidity of the body of gas, and in which the calculated value is converted into electrical signals which are output therefrom.
The enthalpy of humid air is obtained by the following equations (A) and (B) when the temperature and pressure thereof are within the ranges in which every-day air conditioning is carried out. EQU i=0.240t+(597.3+0.441t)x (A) EQU x=0.622h.sub.s .multidot..psi./P-h.sub.s .multidot..psi. (B)
where
t: dry bulb temperature (.degree.C.), PA1 x: humidity ratio (kg/kg'), PA1 P: atmospheric pressure (mmHg), PA1 h.sub.s : saturated vapor pressure (mmHg) at temperature t, PA1 .psi.: relative humidity (%), PA1 i: enthalpy (Kcal/kg'). PA1 a=7.616.times.10.sup.-3 PA1 b=0.2301 PA1 c=-0.06704 PA1 d=0.1634
With equation (B), a complicated calculation is needed in which a value obtained by an approximate expression that has hitherto been disclosed, such as the IFC Formulation for Industrial Use, must be substituted therein to obtain the saturated vapor pressure.
Accordingly, to obtain a value for the enthalpy of humid air using a conventional arithmetic unit it has been necessary to find the value of one other factor, in addition to the dry bulb temperature, as a measured value. That is to say, conventional methods depend on the humidity ratio, wet bulb temperature, relative humidity, and dew point temperature and, whichever method is used, the values measured are converted into enthalpy in accordance with equations (A) and (B) using an electronic computer. Any method depending on finding the dew point temperature or the humidity ratio has the drawbacks of the slow reaction speed and expensive sensing elements, and other methods depending on the wet bulb temperature, relative humidity, and dew point temperature have a disadvantage in that the solving of complicated equations are required.